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ⓘ Chromosomes ..




                                               

Chromosome

The chromosomes of a cell are in the cell nucleus. They carry the genetic information. Chromosomes are made up of DNA and protein combined as chromatin. Each chromosome contains many genes. Chromosomes come in pairs: one set from the mother; the other set from the father. Cytologists label chromosomes with numbers. Chromosomes are present in every cell nucleus with very few and special exceptions. This means they are found in all eukaryotes, since only eukaryotes have cell nuclei. When eukaryote cells divide, the chromosomes also divide. When a somatic body cell such as a muscle cell divid ...

                                               

Allele

An allele is a form of a gene at a particular position on a chromosome. 15 It is the bit of coding DNA at that place. p6 Typical plants and animals have two sets of chromosomes, one set inherited from each parent. 123 These organisms are called diploid. Since such organisms have two sets of chromosomes, they have except on the sex chromosomes two alleles at each gene locus. p6 If the two alleles are identical, the individual is called a homozygote and is said to be homozygous. If instead the two alleles are different, the individual is a heterozygote and is heterozygous. 205

                                               

American Bobtail

The American Bobtail is a breed of cat. It has a short "bobbed" tail about one-third to one-half the length of a normal cats tail. This is because of a genetic mutation that affects the way their tail develops. This mutation also happens with the Manx cat. The American Bobtail looks like the Japanese Bobtail, but they are not in the same cat breed family. The genetic mutations for their bobbed tails are different because the gene for the American Bobtails tail is dominant and the Japanese Bobtails is recessive.

                                               

Aneuploidy

Aneuploidy is a condition where the nucleus of a cell has one or a few chromosomes more or less than the usual number in the species. It is a common cause of genetic disorders. Aneuploidy occurs during cell division when the chromosomes do not separate properly between the two cells. Aneuploidy often causes birth defects and miscarriages. Birth defects make up about 3% of births in the United States. Among those who survive birth, Down syndrome is the most common form of aneuploidy. Many with Down syndrome do survive to adulthood. Some cancer cells also have abnormal numbers of chromosomes ...

                                               

B chromosome

B chromosomes are chromosomes which are not needed for the life of a species. They are also called supernumerary or accessory chromosomes. In addition to normal chromosomes the karyotype, many species have B chromosomes. Wild populations of many animal, plant, and fungi species have B chromosomes. These chromosomes are not essential for their life, and are lacking in many individuals. So a population might have individuals with 0, 1, 2, 3 etc. supernumeraries. Most B chromosomes are mainly or entirely heterochromatic, and so do not code for anything. Some, such as the B chromosomes of maiz ...

                                               

Chromatid

Chromatids are the daughter strands of a duplicated chromosome which are joined by a single centromere. When the centromere divides, the chromatids become separate chromosomes. Each of the two daughter chromatids contains the same DNA and chromatin protein as its original chromosome. But in meiosis, crossing over exchanges take place between two of the non-sister chromatids. This has profound consequences: it produces genetic recombination, and increases the variability of gametes.

                                     

ⓘ Chromosomes

  • Each chromosome contains many genes. Chromosomes come in pairs: one set from the mother the other set from the father. Cytologists label chromosomes with
  • Homologous chromosomes are the pairs of chromosomes in a diploid organism. They are the chromosomes which pair during meiosis. With the exception of the
  • problem with meiosis. When the homologous chromosomes pair in prophase I of meiosis, the genes on the chromosomes pair up. The only way this can happen after
  • development, so making an animal male or female. Normal females have two X chromosomes and normal males have one X and one Y. An egg always carries a single
  • chromosome is one of the two sex chromosomes in mammals. They decide the sex gender of an individual. The other sex chromosome is the Y chromosome
  • B chromosomes are chromosomes which are not needed for the life of a species. They are also called supernumerary or accessory chromosomes In addition
  • Sex chromosomes are chromosomes which determine the sex of individual organisms. In men, for example, there are 23 pairs of chromosomes and one of these
  • sex chromosomes In mammals, the female has two X chromosomes and the male one X and one Y chromosome A karyotype is the characteristic chromosome number
  • has half the usual number of chromosomes A normal eukaryote organism is composed of diploid cells, one set of chromosomes from each parent. However, after
  • Chromosome 21 is one of the 23 pairs of human chromosomes It has 48 million base pairs the building material of DNA This is about 1.5 percent of the